1. Field of Invention
2. Description of Prior Art
Background
Recent studies of hurricane damage on wood-frame buildings indicate that the most extensive destruction to a house by strong winds, was when the roof sheathing was torn off and rain ruined everything in the house.
Roof sheathing ties all the rafters together on a wood frame house, and the roof sheathing tries all the roof trusses together when a masonry or wood-frame house is constructed with trusses. The roof sheathing helps prevent the trusses from racking, or tilting perpendicular to their length.
Sheathing that is tightly secured to the roof and subsequently fastened to the walls, helps transfer uplifting forces to the walls and henceforth to the foundation. If the roof sheathing fails, the trusses collapse, and the walls usually fall down as they can not stand by themselves against strong winds.
Failure and loss of the roof sheathing is common during hurricanes, mainly because of inadequate fastening of the roof sheathing to the underlying structural members. The roof system provides stability to a house by bracing the tops of exterior and interior load-bearing walls.
Sheet metal joints perform better than nailed joints in high winds and during seismic activity. Strong connectors, secured by well placed fasteners, will insure that the major structural members of a house are securely tied together.
Hurricanes
Studies of damage after Hurricane Andrew show several problems with the attachment of roof sheathing that this invention solves. Some sheets of roof sheathing that were blown off houses contained no nail holes, indicating that the sheet was placed in position, but was not nailed down. Some roofing sheets had nails in them that had missed the rafter that they should have been nailed upon. Some sheets had staples or nails that had rusted away, and on some sheets the nails had just pulled out from the rafter.
The engineering staff of the American Plywood Association provided technical personnel to assess the damage from Hurricane Andrew in Florida. The majority of wood structural sheathing failures were attributed to improper connection details, and in every case investigated, the sheathing loss was a result of improper nailing (Keith, 1992).
These problems have not been solved because staples are still used to tie down roof sheathing, and by looking at new construction, nails are still seen poking through the roof sheathing, completely missing the roof rafter. Most conscientious framers would drive another nail when they felt the nail miss the underlying rafter, but with the new powered nail guns, the framer can not tell if the rafter was missed because each shot feels the same, no matter what the nail is being driven into.
Earthquakes
During an earthquake, the floor, wall, and roof diaphragms undergo shearing and bending. The shear forces from the roof boundary members are transferred to the top of the shear wall by way of toenails or blocking to the top plate. To withstand and transfer the shear loads, plywood sheets have to be spliced together to prevent adjoining edges from sliding past or over each other (Gray, 1990).
Butted together on the centerline of a 2xc3x97 (nominally 1xc2xd-inches-wide), you""ve only got xc2xe inch bearing for each plywood sheet, so the nail has to be xe2x85x9c inch from the edge. This leaves little margin for error, and nailing has to be done with care to avoid splitting the plywood and missing or splitting the underlying member (Gray, 1990).
Tests at the University of California show that plywood secured by overdriven nails, nails that penetrated the plywood beyond the first veneer (usually by a powered nailgun), failed suddenly and at loads far below those carried by correctly nailed plywood panels (Gray, 1990).
Steel connectors, between different components of a wood-frame building""s superstructure, provide continuity so that the building will move as a unit in response to seismic activity (Yanev, 1974).
Prior Art
A number of connectors have been developed to tie together the structural members of a house under construction. Up until this invention, nobody had seen how to make a compact connector that could tie two or more sheathing sheets together and to the underlying structural members, or could be applied from the top of the roof.
Some prior art prevents uplift, but this invention not only prevents uplift during hurricane-force winds, but prevents lateral movement during earthquakes.
A previous sheathing tie that wrapped around a structural member and attached to the sheathing by a different method, is on application Ser. No. 09/227059 sent in Jan. 7, 1999.
The Simpson Strong-Tie Co.""s January 1996 catalog (page 62) lists a PSCL Plywood Sheathing Clip. This clip provides a gap and aligns sheathing but does not tie the sheathing to underlying structural members or prevent uplift or lateral movement. No other sheathing ties were found in their catalog, but they do show several seismic and hurricane ties on pages 60-61.
Several of their ties xe2x80x9cneck downxe2x80x9d at right angle bends. The H2, H2.5, H3, H4, H5, and H7 become narrower at their right angle bends. This is also seen on the flat pattern layout for the H4 and H5 on U.S. Pat. 4,714,372 by Commins. The xe2x80x9cnotch effectxe2x80x9d shown in this patent is also avoided on my invention because of the smooth bends and edges.
A prior art roof securing system by Llorens, U.S. Pat. No. 5,390,460 ties down a single sheet of roof sheathing to a support beam. This is a good connector, but it is long, and can only tie down one-size of sheathing. It must be hammered around the beam from below, but panels are installed from above the roof. Llorens"" 460 can only tie down one panel and provides little lateral support.
Another sheathing strap and alignment guide by Nellessen, U.S. Pat. No. 5,423,156 shows an apparatus for securing sheathing using a long strap, connecting bands, and saddles. This is a good connector, but it is long, complicated, and must be installed from below the roof. With sheathing in place, this is difficult. Nellessen""s 156 can only tie down panels of one size.
According to Fine Homebuilding, October/November, 1998, sheathing courses should begin with either a full or half sheet. The course of sheathing at the top row and beginning row are often odd-size, in order to get a reasonable width of sheathing on the top row. The above can""t tie down odd-size sheets.
Accordingly, several objects and advantages of my invention are that it helps secure the roof, wall, and floor of a building to keep the building from being destroyed by hurricanes, tornadoes, and earthquakes.
This invention helps prevent the wall of a building from detaching from the wall studs during a hurricane or earthquake. It makes the wall into a stable shearwall, transferring shear forces into the foundation and ground.
This invention helps prevent the roof of a building from detaching from the rafters or roof trusses during a hurricane. It ties the roof sheathing securely to the underlying rafter or roof trusses, transferring lateral and uplift forces to the walls and to the foundation.
This invention helps prevent the floor of a building from detaching from the floor joists during an earthquake. It makes the floor into a horizontal shear wall, and helps the floor resist lateral forces in its horizontal plane. It also makes sure that any forces transferred from the roof and wall can be managed by the floor and transferred properly to the ground.
One object of this invention is to make each plywood structure on a house into a shearwall, that is, able to transfer forces without breaking or disconnecting. By tying the plywood securely to the underlying structural member, the plywood can reliably transfer and dissipate shear, lateral, and uplift forces to the ground.
During an earthquake or a hurricane, another object is for the building with my invention to move as a sturdy unit, resisting and transferring destructive forces to the ground. Mounted on the roof sheathing and rafter, my invention resists uplift, the most destructive force during a hurricane. Mounted on the wall stud and wall sheathing, my invention prevents the wall sheathing from being blown off or sucked out by the extreme negative pressure of a hurricane. Mounted on the floor sheathing and floor joists, my invention prevents the floor from separating, if it should get wet during a hurricane.
During an earthquake, when my invention is mounted on the roof, walls, and floors, they will turn each member into a shear wall. The secured plywood will absorb and dissipate earth movements, without becoming detached from the underlying structural members. It will also prevent the sheathing from sliding over or past each other.
This could improve a house to existing building codes, as sheet metal joints have been proven to perform better than nailed joints during hurricanes and earthquakes.
Another object of this invention is the large surface area on the top or outside part of the sheathing. This area prevents the plywood sheathing from splitting during nailing. The large surface area provides more strength in the hold-down process.
Still another advantage is the accurately placed nail holes on the invention. These nail holes prevent nails from splitting the plywood or underlying rafter, stud, or joist, by making the framer place nails at the correct and accurate location.
Another advantage is that the invention prevents overdriven nails from penetrating the fragile outer veneer of the plywood sheathing. The accurately placed nail holes prevent the nailhead from piercing the outer veneer of the plywood.
Another advantage is that some nails, on the invention, are driven into the strong broad side of a rafter, stud, or joist, forming a very strong connection to the sheathing, preventing the nails from pulling out.
Yet another advantage of this invention is during earthquakes, nails can sometimes bend with the movements of the house, but screws often break. Even though screws hold tighter than nails and provide a tight connection against uplifting forces from hurricanes, they are less resistant against earth movements. This invention absorbs and transmits most of the forces during an earthquake and hurricane so nails and/or screws can be used as fasteners.
Another advantage is that since the invention absorbs and transfers earthquake and hurricane forces, less nails and nailing could be used. Also, screws could be used in the invention in earthquake areas with less fear that the heads will shear off.
Still another advantage of the invention is in the ability to prevent plywood sheets from sliding past or over each other during an earthquake. Previously, only nails had to shear, but this entire connector must be sheared for the plywood to slide.
Another advantage is that plywood panels should not be butt together tightly or they may buckle when they expand due to heat or humidity. A slight gap should be left between panels. This invention provides a slight gap next to each plywood panel that the invention is installed upon.
Still another advantage is that with the roof sheathing firmly attached to the rafters, roofing material will have a better chance of staying on during strong winds and earth movements. In addition, with the sheathing firmly connected, new materials may be attached to the roof, such as solar electric panels, without fear of them being blown off.
In areas with brush or forest fire danger, fire-proof material or heavy material, such as tile, stone or metal, can be applied to the roof with less danger of being blown or shaken off during earth tremors or high winds.
When the invention is applied to the studs and wall sheathing, fire-proof materials such as stucco or brick veneer can be applied to the sheathing with less chance of being shaken off during earth movements.
When the invention is applied to the floor joists and floor sheathing, the interior load-bearing walls can have a horizontal shear wall, inside the house, to help transfer earth movements.
Earth tremors and hurricanes always destroy the weakest parts of a house. By making each envelope of a house, the vertical walls, horizontal floors, and roof envelope into a strong unit, there will be less damage.
Another advantage is that the building contractor or a building inspector can visually inspect the roof sheathing, wall sheathing, and flooring for correct tie down, and can be assured that all the nails have been correctly placed. Previously, a visual inspection could not determine if the sheathing or flooring was properly applied and secured.
Still another advantage is that the invention can hold down standard-size or odd-size sheathing. According to Fine Homebuilding, October/November, 1998, sheathing courses should begin either with a full or half sheet. The course at the top row and beginning row are often odd-size, so that a reasonable width of sheathing is on the top row.
An advantage is that the framer can more accurately determine where the underlying structural member is located because the tie is on top of the sheathing, in line with the member.
Another advantage is the invention is easily used with current framing methods. The invention is installed from the top side of the sheathing so the framer doesn""t have to go under the sheathing, which can be dangerous.
Nailguns can be used to attach this invention if the nail protrudes from the gun, prior to being driven. Nailguns can be used to apply nails to the sheathing and underlying rafter in-between the installed inventions, just like conventional construction. Screw guns can be used as well.
Still another advantage of this invention is when it is applied to the floor joist and floor sheathing, it will keep each sheet of sheathing a slight distance from each other helping prevent squeaks. Also, after a house is built, the wood floor joists and plywood shrink at different rates, causing gaps between them. By being tightly secured with my invention, any gaps will be insignificant, averting any squeaks.
Still another object is that the invention is thin so that a covering or underlayment can be easily applied. There is no xe2x80x9cnotchxe2x80x9d effect where sharp corners or bends can cause stress points. All bends and edges are smooth. The rafter web, offset web, and sheathing web are constant width for strength.
It is a further object of this invention that it easily, quickly, and economically protects houses from the destructive forces of earthquakes and hurricanes. It is a still further object that the connectors and fasteners are strong, attractive, permanent, functional, uncomplicated, simple to manufacture, easy to install, and economical. All of the embodiments can be made from a single sheet metal blank, without any welding.
A further object is that this invention can be used on various size sheathing, rafters, roof trusses, studs, wood or metal I-beams, all made from wood or metal. There may be insurance discounts for homeowners who have this invention installed on their houses.
Previously, architects, engineers, and builders did not know how important the attachment of plywood sheathing was to the roof, walls, and floors. It was thought that the weight of the roof would keep the sheathing attached during a storm. Prior to this invention, no thought had been given to the floor as a horizontal shear wall during an earthquake.
Older homes were built with rafters 16-inches-on-center, but newer homes are built 24-inches-on-center. This means there are less nails per sheathing sheet than before. The holding power of this invention more than compensates for the less nails. Adhesive foam has been used to hold down sheathing, but it can shrink and lose holding capacity. Another advantage is this invention will last the life of the house, with full holding capacity.
A further advantage of this invention is that different thicknesses of sheathing can be attached using the same component. There is no need to buy different types of clips for houses using different thicknesses or density of sheathing, because this invention will work with any depth including metric.
This invention will hold down any thickness of wood sheathing, metal sheathing, composite sheathing, or insulating sheathing using just one single type of component. This saves manufacturing, shipping, and inventory storage of components, since one size fits all. The invention nests during manufacture, saving metal, and nests during packaging, saving space.
Another advantage is that this invention can hold down different thickness of sheathing to different width structural members such as 2xc3x974""s, 2xc3x976""s, 2xc3x978""s, etc. It can securely hold sheathing to solid wood members, trusses, hollow beams, engineered beams, and laminated beams. The invention works on beams that are horizontal, vertical, or sloped.
These and other objectives of the invention are achieved by a simple and economical connector that allows a builder to quickly and easily secure sheathing to structural beams, making a building resistant against earth tremors and high winds.
Advantages will be discussed in the description. Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.